A car bomb killed the head of the anti-terror force in Yemen's restive southern Abyan province, a Yemeni security official said.
Three others, including two children, were wounded in the blast that killed Ali al-Haddi near the coastal city of Aden. The bomb was planted in al-Haddi's car, the official said.
Security has broken down across Yemen during the nine-month popular uprising against autocratic President Ali Abdullah Saleh, who has ruled the country for more than 30 years. Demonstrations raged around the country on Friday.
Al-Qa'ida-linked militants have taken over a number of towns in Abyan, along the country's south coast, where they regularly engage in deadly clashes with security forces. Yemeni authorities also accuse them of targeting security officials.
The official spoke on condition of anonymity because he was not authorized to talk brief the media.
Tens of thousands marched in anti-government demonstrations across Yemen Friday. Protesters have been on the streets nearly every day since January, despite a bloody government crackdown.
In the central city of Taiz, security forces opened fire on marchers carrying the bodies of protesters killed in recent days, wounding five people, activists said.
Thousands also marched in the capital Sanaa, where government troops have been clashing with army defectors who have joined the protests and armed men loyal to Yemen's most powerful tribal chief, who supports the opposition.
A medical official said a 28-year-old woman was killed in crossfire in Sanaa during a gunbattle between the two sides. The official spoke on condition of anonymity because he was not authorized to speak to the press.